Production of ammonium phosphates



. ed with an of the tri-ammonium phosphate is precipi- Patented Sept. 27, 1932 UNITED TATE PATENT OF I E- 4 JOSEPH GUILLISSENjOF isnnssnnsf BELGIUM, nssronon T Union cnmrounianmn socrnrr: AYNONYME, or BRUSSE V LS, BELGIUM V rnonucrronor AMMONIUM PHosrHArEs Application filed December 20, 1929, Serial No. 415,623, and

' '7 This invention relates to an improved proc ess for the production of ammonium phosphates, more particularly of triammonium phosphate, which permits of reducing the costly operations of evaporation of solutions of phosphoric acid or of mono-annnonium phosphate, which are unavoidable inother known processes, and :to obtainin an easy manner, a pure tri-ammoniumphosphatefree from impuritiessuch as iron'salts, alumina and lime.

The invention consists-in a process for ob.

taining pure tri-ammonium phosphate by the reaction between an excess of ammoniaand a solution of phosphoric acid containing impurities such as iron salts, alumina and lime, in which the solution is saturated partly with ammonia until the impurities are precipitated, the precipitate being thereupon separated 7 from the solution, the latter being then treatexcess of ammonia until the bulk tated. I I

When gaseous ammonia is used, it can be subjected to expansion, prior to its admission into the solution with a view to precipitating the tri-ammonium phosphate; the expansion of the ammonia is carried out in' a -su'itable vessel so situated relativelyto the vessel containing the phosphoric acid or phosphate solution, that the latter solution is cooled.

For the purpose of making my invention more clearly understood I have shown in the accompanying drawing means for carrying the same into practical effect without limiting the improvements in their useful applications to the particular method, which, for the purpose of explanation, has been made the subject of illustration. 7

The single view disclosed in the. drawing is a diagramatic representation of a flow sheet for carrying out the method forming the subject matter of the invention.

As may be noted the, reference numeral 1 denotes a suitable absorber for containing the phosphoric acid solution undergoing in Germany, France, and Great Britain lebiuary 22, 1929. V Y

treatment. Gaseous ammonia after expansion ina duced into the absorber 1. Prior to admitting the ammonia ble ammonium phosphoric acid solution or may be addedthereto for a suitable expansion device 2 is introgas' into the absorber solusalts are introducedinto the sulphuric acid purpose which will hereinafter appear.

A sufficient amount duced into the absorber of ammonia is introto cause the precipitation of the impurities contained in the phosphoric ac means of conducted into a second id which are separated therefrom by a suitable filter 3, the filtrate-being absorber 4, Where it isvsaturated with gaseous ammonia after expansion in a suitable. device 5..

Th sults e' se cond saturation of the solution rein the formation of tri-ammonium phosphate which is separated therefrom ina suitable separating device 6,-the filtrate or. mother liquor being freed from ammonia which may be used 0 After phosphate,

and may a suitabl temper-at ver again or the mother liquor is the circuit for diluting the phosseparation of the tri-ammonium which is inthe crystalline. form, be conducted. from the separator to e container or vessel. 7 it may be treated 'with a mineral acid, such as phosphoric acid or an air current at a suitable ure maybe passed through it to decompose it into bi-ammonium phosphate. 1

l The table givenbelow shows the results of a' series of eleven tests made at a temperature of C.

The first column gives the number of the test, the second column gives the total amount gives the which "is r of free ammonia (grams per liter) in soluthird column gives the P 0 grams in solution, the fourth column NH corresponding to the P 0 necessary for the formation of pure (NH;) PO and the fifth column gives the NH, whi

0b is missing or in excess relatively rev to the amount necessary for the formation of (NI-I PO (that is, the difierence between the figures given in the second and in the fourth column).

I 11 111 IV V H NHa puis- N a coring g- ,3 t respondor in Numg? f E ing to excess g g solution solution v 3:; ai grams grams monium formation per liter per liter phosphate of (NH4)3PO4 1 33. 72 47. 81 34. 38 i U. 66 2 34. 78 34. 46 24. 78 +10. 3 33. 72 32. 87 q 23. 54 +10. 0 4 36. 54 25. 19 18. 12 +18. 42 37. 74 22. B6 16. 44 +21. 30 6 43. 02 2Q. 14. 46 +28. 55 7 49. 72 17. G0 12. 66 +37. 06 8 65. 60 10. O1 7. +58. 9 81. 7O 6. 59 4. 74 +76. 96 10 92. 88 5. 34 3. 84 +89. 01 11 316. 00 0. 20 0. 14 +315. 86

It is seen that according as the excess of ammonia increases, the amount of P 0 which remains in solution, diminishes. For an excess of ammonia (test number 11) of +'315.86, the amount of P 0 which remains in solution is only 0.20 grams per liter.

In practice, it is of course not'always necessary to carry the precipitation of the phosphate so far. The proportion. of tri-ammonium phosphate to be precipitated is determined in practice according to the respective prices of ammonia and of phosphoric acid.

For the carrying of the invention into effect, use is preferably made of a diluted solution of phosphoric acid.

The major part of the solution separated from the precipitated tri-ammonium phosphate may be used direct for diluting the acid used in the manufacture and may thus be left in the circuit.

It has been found by experience that the presence of soluble ammonium salts, such as the sulfate facilitates the precipitation of triammonium phosphate. The said salts may be added to the solution prior to the admission of ammonia or they may be formed inside the solution by the admission of a suitable acid, such as sulphuric acid. 7

Thus, by adding aqueous sulphurioacid, sulfate of ammonium is formed inside the solution, and the insolubility of the tri-ammonium phosphate is increased, thus facilitating its precipitation.

The solution may be thrown away without great loss, after its ammonia has been recovered, or the small quantities of phosphoric acid which it may contain, may be recovered, if necessary, by precipitating them in the form of bi-calcium phosphate. Thisremoval of ammonia from the residual liquor may be efiected in an ordinary cast-iron or iron apparatus, whilst the evaporation of phoscertain cases phoric acid or of mono-ammonium phosphate in the known processes required costly apparatus made of materials which resist to corrosion by the said substances.

The tri-ammonium phosphate obtained after separation by centrifugal action, may be dried at a suitable temperature in a current of air, which decomposes the tri-ammonium phosphate into bi-ammonium phosphate and free ammonia, and the latter may be utilized for saturating a fresh amount of phosphoric acid.

- q Incertain cases it has however been-found;

advantageous to obtain the bi-ammonium phosphate by treating the tri-ammonium phosphate, in a crystallized, dry state, with a concentrated solution of phosphoric acid of P 0 forinstance).

The phosphoric acid may be replaced in centrated sulfuric acid. m V

The addition of phosphoric acid containing 50%" of P 0; converts tri-ammonium phosphate into bi-ammonium phosphate and theamount of water introduced by the acid, dissolves until saturation point, part of the bi-ammonium. phosphate produced.

Although: this solubility is high, a small portion only of the bi-ammonium phosphate is dissolved because the amount of water brought in is very small. V

' As a consequence th of bi-ammonium phosphate produced is not dissolved and may be separated from the saturated solution by turbining or filtration.

The small amount ofsaturated solution of bi-ammonium phosphate may be dried without the necessity of employing a complicated apparatus as would be required for decomposing the tri-ammonium phosphate so as to recuperate in the latter case, it is difiicult to conduct the operation so as to obtain pure bi-ammonium phosphate without mono-ammonium phosphate.

Ewample One kilo of a solution of phosphoric acid obtained by treating a natural phosphate with sulphuric acid, and containing 280 grams of P 0 is diluted with 600 cc. of water, then saturated with a current of ammonia until the salts of iron, alumina, lime etc. which it contains, are precipitated. The solution is filtered and the precipitate is washed. The filtrate and water used for washing weigh together about 1700 grams. This liquor is saturated again by a current of NH until the solution contains an excess of about 9% of free ammonia (see test number 10 of the table) +8904 grams per liter of free ammonia. About '800 grams of tri-ammonium phosphate are precipitated and the mother liquor separated from the precipitate weighs about 0.9 kilo of which 0.6 kilo are used for by another acid, such as. conthe ammonia evolved. Moreover,

diluting a. fresh kilo of phosphoric acid and 0.3 kilo are boiled for liberatin V nia. By admitting that the P 5 contained in the 0.3 kilo of liquor are lost, this would represent (see test number 10, third column of the table) 5.34X0.3=1.602 grams of P 0 from the original 280 grams.

I claim:

A process for obtaining solid, pure, stable di-ammonium phosphate, consisting in treating dry, crystallized, tri-ammonium phosphate with the calculated quantity of a concentrated solution of phosphoric acid in order to produce the di-ammonium salt; and then drying the cation of heat.

JOSEPH GUILLISSEN.

the ammoproduct without the appli- 

